High technology, particularly electronics technology has known a rapid, spectacular development in recent years. As such, a wide variety of new electronic products are available in a fast pace. A unique one of the new electronic products is cellular phone having advantages of compactness, multi-function, and easy operation. Cellular phones also have characteristics of being lightweight, slim, and advanced. Thus, it is obvious that cellular phone is the most important one of the wide variety of new electronic products.
Conventionally, backlight device is only provided in a keypad of a cellular phone. The backlight device is adapted to enable or disable in a simple way. For example, a user can press any key of the keypad to enable the backlight device irrespective of day or night. Light is thus emitted from the enabled backlight device.
The above technique can solve the problem of being unable to see keys of cellular phone clearly in the night or dark environment by emitting light by activating the backlight device. However, control of the backlight device in the keypad is disadvantageous because it is done by manually enabling or disabling the setting. As such, many users frequently experienced tediousness and inconvenience in setting the activation or deactivation time of the backlight device. As a result, it is frequent that the backlight device of a cellular phone is always in an enabled state irrespective of day or night.
However, electric energy of battery of a cellular phone is consumed significantly because the backlight device is in an operating state for a long period of time even in a bright daytime and also the cellular phone is frequently used. As a result, both standby time and operating time of the cellular phone are shortened greatly.
Thus, it is desirable to provide a method of automatically enabling or disabling backlight of a cellular phone based on a predetermined time in order to overcome the above drawbacks of the prior art.